Impregnation of electrical condensers



awed Feb.'28,1 933 y UNITED STATES PATENT OFFICE mx xnvansox, or raw YORK, 11. x. nnmmiu'rron or uncrnrcan counnnsnas Io nnwmg. Application filed my,

My present invention relates generally to electrical condensers and has particular reference to the impregnation of condenser bodies of the so-called paper dielectric type.

Condensers of the character to which my inviention has particular reference are gen era 1 ductive and non-conductive material. For example, foil might be interwound with strips of paper or similar impregnable and non-conductive material, the wound condenser body being subsequently compressed into a substantially flattened shape, suitably treated for purposes of drying, and impregnated with a dielectric material.

It is a general object of my present invention to rovide an electrical condenser body of the ibregoing character wherein an improved impregnating material, in the form of a novel composition of matter, is employed,

. It is well known that the impregnating medium is of paramount im ortance in producing a condenser of hi efiiciency. An ideal condenser body woul be totall devoid of an non-conducting material suc as paper, the strips of paper or the like being employed simply for practical reasons in facilitilting the pro er interwinding and mutual insulation of t e conductive strips. Accordingly, it is highly desirable to im regnate the condenser body with a material having a high dielectric constant, which is not too .expensive, and which lends itself readily to thorough impregnation throughout the entire condenser body and particularly throughout the fibers of the paper or similar insulating strips. I

Besides a high dielectric constant, it is necessary that the impregnating material be one which does not too easily permit the passage therethrough of leakage current. The socalled breakdown of condensers of the character to which this invention relates is a phenomenon the causes of which are not fully understood. Thus, condensers may fail in certain cases because of what is believed to be an excessive void formation and internal ionization. In other cases, failures formed by interwinding layers of con-' 1828. Serial No. 865,783.

may be due to physical leakage allowing entrance of air or moisture. 11 many instances, breakdown has been found to be the ultimate result of some sort of heat phenomena, the unwinding of a broken-down condenser often disclosing holes with burnt or charred edges. Besides having a high dielectric constant, it is therefore desirable that the impregnating material be one which prevents, to the maximum possible degree,premature breakdown, whatever the exact cause may be.

It is'a more particular'object of the present invention to provide an impregnated condenser of the foregoing character wherein the impregnating medium is such that the likelihood of breakdown, even at relatively high voltages, has been minimized, and

wherein the life of the condenser has thereby been considerably increased.

The employment of oil has comparatively recently found favor as an impregnating medium for condensers of the type herein referred to.. It has advantageous and desirable characteristics of long life,,probabl due to the fact that its sustained liquid con ition facilitates the dissipation of heat induced by minute leakage currents. Furthermore, its liquid condition serves to reduce the formation of undesirable voids. And not only is its own conductivity for leakage currents in many cases less than that of the wax customarily employed for impregnation, but it does not absorb moisture to any appreciable degree, and its leakage conductivity is thereby not increased with time as is frequently the case with wax, as, for example, parafline.

One of the features of my invention resides in the employment, as an impregnating material, of an oily substance or composition of matter whereby the foregoing advantageous characteristics are made use of. One of the disadvantages of oil lies in the fact that its normall liquid condition renders it less cohesive than a relatively solid material. such as wax, and as a result, it is not as efiicacious in firmly holding the layers forming the condenser body in close superposition. Accordingly, although its dielectric strength may be substantially the same as that of wax or the ascents like, has proven comparatively expensive oil might be offset by its correspondingly as compared with wax. high leakage current conductivity. I have An important object of my present invenfound, however, that the normally high leaktion is to provide an improved composition age. current conductivity of the castor oil of matter tor the impregnation of condenser seems to disappear entirely when aiblending bodies wherein the advantageous characterisor .intimate intermixture of the foregoing tics of oil are maintained while the dielectric character has, been effected. As a matter of constant has been sufliciently increased to renfact, the resultant oily composition of matder the employment thereof highly advantater acts in many ways as a pure mineral oil 1 geous from. all standpoints, including that'o'f having no less resistance to the passage of 7 manufacturing cost. leak'age-acurrents than that of pure mineral Briefly, my invention resides in theemoil. On the other hand, however, I have ployment of at least two difierent oils capable "found that "the oily compound of these two of mutual. intimate intermixture thereof, oils has a dielectric constant considerably suitably inexpensive and available on the higher than thatof the mineral oil by itself. 80

market so as to render the commercial ems For example, dependingentirely upon the ploymentrthereof feasible, and imbued with proportionsin which the two oils are intercharacteristics which complement each other mixed, the resultant'composition of matter in the production of a highly ellicient and may becaused to embody adielectric constant 'relativelyinexpensive condenser of great of anywhere from 2 to 4.

strength and'long life. i ln carrying the invention into practical From one aspect, the invention resides in effect, the. condenser bodies are formed or the employment of mineral oil in combination -wou'n d in thecustomary manner and vacuumwith a second and different type of oil which treated and dried in accordance with wellcomplements the mineral oil and produces a kn wn'p a t -lhey t 1 i p g 99 resultant composite oily composition of matwith theoomposite oil resulting from an in ter of highly desirable characteristics so far t mate intermixture of blending of mineral as the impregnation of condensers is conand caster oils. 1 have found an intermixcerned. More specifically, I employ a secture in the proportion of 6070% of castor end oil which has a relatively high dielectric oil and '30 /0 of mineral oil to be highly 5 constant, which would be wholly unsatisfacsatisfactory, the product having a dielectric tory for use by itself, and which blends neverconstant of approximately 3.5 and a leakage theiess with mineral oil in such a manner that rrent conductivity no greater than that of a the ultimate intermixture embodies all the ordinary mineral oil.

35 desirable characteristics of mineral oil, and S ate otherwise, the mixture produced in 100 in addition, a relatively high dielectri accordancewith my invention is one wherein strength and on tant. I I the advantageous characteristics of the min- More specifically, l have found that caster ral 011 have beenretained, wherein the adoil is suitable for my present pur ose All vantageous high dielectric constant of castor 1 .1; v getable oils seem to have a high leakag oil has materially contributed to an increased conductivity and are therefore unusable by dielectric constant of the mixture, and wherethemselves for electrical purposes. Castor oil in e j c i nfible'leakage current conducno exception in this respect since it has a tively initially present in the pure castor oil considerable afinity for moisture; but it asas app n y Vanished, at least so f r as an surnes importance from the standpoint of my increase of leakage Current conductivity of present aims and objects by virtue of the fact h re tant in ermiXtur-e is concernedhglhe that it has a very high dielectric constant, advantages of such' an impregnating medvia, approximately a as distinguished from Him n d hardly l e 1 7 the average dielectric constant 2 of mineral By the term l as the m is employed herein and in the appended claims,

Although'mineral oil and castor oil will it Wi e u e o h Prefer to any not ordinarily blend, it is possible neverthena ur l f t p tr eum Series, Such as p less to cause an intimate intermixture thereof p -ba n p -ba e 0 le nein a number of ways. For ex l b i base oil, or combinations of these oils. Any

several hundred degrees centigrade under y g y P invention. l

pressure, a suitable blending ma be efiected. 1 d0 no m to limit my lf t0, ny P Ap ar ntly, th a to il p0 ymerizes cific proport ons of the two ingredients nor such anianner that the two oils willmixin all o y pa cular m nner of blending the ilgjfiyp'g ijgwg d ill remain i inti at same, except insofar as either'of these factors blended relationshi even. after the temperais essential to produce the advantageous retnre subsequent y been reduced to normal sult desired.

eondafion. Y i lngeneral, it will be obvious that changes M; it might appear that the advantage gained in the details herein described for the purby the high dielectric constant of the castor pose of explaining the nature of my inveni th a d i i th temperature t oil of this general class may be employed'in I tion may be made by those skilled in the art without departing from the spirit and scope of the invention as ex ressed 1n the appended claims. It is there ore intended that 5 these detailsbeinterpreted asillustrative and not in a-limitin sense.

Having thus escribed my invention, what I claim as new and desire to secure by Letters Patent is- I m 1. As a new article of manufacture, an

electrical condenser in which the dielectric employed therein comprises a mineral oil and castor oil blended substantially as described.

16 2. As a. new article of manufacture, impregnated electrical condenser bod In which the dielectric impregnating m ium comprises an intimate intermixture oftwo oils, one of which has a relativelv low di- 20 electric constant and; a relatively high dielectric resistance, the other of which has a relatively high dielectric constant and a relatively low dielectric resistance, whereby said body is impregnated with an oily medium embod ing the advantageous electrical qualities 0 both oils.

3. An electrical condenser body comprising alternate layers of conductive and nonconductive material and impregnated with an oily dielectric medium com rising an intimate. intermixture of castor 011 and mineral oil in the proportion of approximately 601-707;; of castor oil to 40-30% of mineral o1 35 4. As a new composition of matter for the impregnation of electrical condenser bodies an intimate inter-mixture of castor oil and mineral oil, said oils being blended as the result of heating thereof under pressure.

In witness whereof I- have "signed this specification this 20th day of Ma 1929.

MAX KE LSON. 

